1. Field of the Invention
This invention relates to a method and apparatus for detecting a control signal and more particularly to such a method for detecting an identification signal in a digital signal reproducing device.
2. Description of the Prior Art
Recently, in association with the progress in the art of signal processing, it has become customary to record control signals concerning record contents or the operating conditions simultaneously with the recording of audio or video signals on the recording medium. For example, in a rotary head type digital audio tape recorder or so-called R-DAT, record tracks are formed obliquely on a magnetic tape used as the recording medium, and control signals called sub-code signals are formed in a sub-code area on each track in addition to the audio PCM data per se.
The control signals recorded in the sub-code area include start identification or start ID signals indicating the start of the recorded program. For example, in the leading part of a program, such as music, the start ID bits of "1" are recorded for an interval of 9 seconds, so that finding the leading part of a number or program searching can be done by detecting these start ID bits at the time of reproduction.
In these R-DATs, the error rate becomes rather high during high-speed searching, such as during 200-times normal speed searching, so that it becomes extremely difficult to read out the control signals including the aforementioned start ID signals.